1. Field of the Invention
The present invention relates to a method and apparatus for controlling the fuel-injection amount in a diesel engine in which a fuel-cutting operation is performed when a rotational angle sensor for detecting the engine speed is in an abnormal state.
2. Description of the Prior Art
Generally, in a diesel engine, the fuel-injection amount is calculated basically dependent upon the engine speed and the accelerator opening. However, when the rotational angle sensor for detecting the engine speed is in an abnormal state, the fuel-injection amount is calculated basically dependent upon only the accelerator opening. In addition to this, when the vehicle speed is in the vicinity of 0 and the accelerator opening is in the vicinity of 0, a predetermined delay time period, such as 1 msec, elapses so that a fuel-cutting operation is performed, thereby indicating to the driver that the rotational angle sensor is in an abnormal state.
In the above-mentioned prior art, however, if the delay time period for the fuel-cutting operation is set to be relatively short, stalling of the engine may often occur even after the engine has been restarted. In such a case, therefore, if the engine stalls when the vehicle is temporarily stopped at an intersection, it is difficult to move the vehicle to the shoulder of the road. On the contrary, if the delay time period for the fuel-cutting operation is set to be relatively long, even when the driver, who is unaware of the fuel-injection-amount control when the rotational angle sensor is in an abnormal state, lets up on the accelerator, the fuel-injection amount when the rotational angle sensor is in an abnormal state may be larger than the fuel-injection amount when the vehicle is in a conventional idle state, thereby increasing the vehicle speed beyond expectation, which is a disadvantage.